1. Field of the Invention
A subject of the present invention is a material, in particular metallic, the surface of which is modified, as well as its preparation method. The present invention also relates to the uses of said material, in particular for the preparation of implants, stents or prostheses.
2. Description of the Related Art
The covering of metallic surfaces by organic layers constitutes a set of significant industrial methods (Plankaert, 1994; Biethan et al., 1991; Hochberg, 1979). These methods involve the deposition of a polymer on a metal sheet, either from a liquid, or from a solid polymer sheet or also by cataphoresis. In these methods, only weak bonds are formed between the metal and the organic layer. Other methods have been described, they also involve weak bonds for example during the deposition of polyphenols on Pt (McCarley, 1990), in the electrochemical deposition of conductive polymers in particular on iron (Lu et al., 1988; Cheung et al., 1988; Troch-Nagels et al., 1992; Schirmeisen et al., 1989; Beck et al., 1994; Otero et al., 1992; Ferreira et al., 1990; Ferreira et al., 1996; Krstajić et al., 1997; Su et al., 1997; Fraoua et al., 1999).
Two types of methods exist for creating stronger bonds between the metal and the organic layer: in the first type a bond is formed between the organic layer and an oxide on the surface of the metal (Biethan, 1991; Hochberg, 1979; Boenig, 1984; d'Agostino, 2000; Vautrin-Ul et al., 2000), and in the second type, bonds are formed between the metal itself and the organic layer.
Several electrochemical methods already exist which make it possible to attach polymers to metallic surfaces using covalent bonds. Polymer layers can be attached to platinum by oxidation of N-vinylpyrrolidone (Doneux et al., 1997; Calberg et al., 1998). Moreover, the electrochemical oxidation of amines leads to the grafting of —NHR units onto the platinum. By using ω-diamines such as ethylenediamine, it is possible to attach polyethyleneimine to Au, Pt or Al (Herlem et al., 1997; Herlem et al., 2000; Fahys et al., 2002; Herlem et al., 2003; Lakard et al., 2002). However, it should be noted that the methods using the electrochemical oxidation of organic substrates are not applicable to industrial metals which are in general very easy to oxidize. Methods using electrochemical reduction are therefore particularly desirable. One of these methods (Lécayon et al., 1982; Deniau et al., 1992; Viel et al., 1993; Bureau et al., 1994; Tanguy et al., 1993; Tanguy et al., 1994; Tanguy et al., 1996; Deniau et al., 1997; Bureau et al., 1997; Deniau et al., 1998; Charlier et al., 1999; Viel et al., 1999; Jérome et al., 2001; Baute et al., 1999; Mertens et al., 1998; Calberg et al., 1997) involves reducing an active acrylic monomer onto a metallic surface (for example of nickel or iron). The radical-anion formed under anhydrous conditions is responsible for the reaction with the metal and for the continuation of polymerization. A fine layer of polymer (2 to 10 nm) is attached in a covalent manner onto the surface. At the same time, a thicker layer of polymer is only deposited, it can be eliminated by rinsing.
Several methods for grafting preformed polymers onto a functionalized surface (“grafting onto”) have already been described making it possible to attach polymers to a polyaryl under-layer obtained by the electrochemical reduction of diazonium salts. The first method consists of grafting onto the metal a benzophenone unit which reacts with the polystyrene under photochemical irradiation; the second method consists of grafting a benzoic acid unit, which can react with magnesium ions and the free carboxylic groups of a polyester deposited mechanically onto the surface (Adenier et al., 2002). A method which is similar to the first two has also been described (Lou et al., 2002), involving grafting polyesters comprising pendant acrylate groups by electrochemistry. The poly-ε-caprolactone thus grafted being miscible with poly(vinyl chloride), the PVC layers thus obtained are strongly adherent.
Several “grafting-from” type methods have been developed which make it possible to make polymers grow from a functionalized surface. On an iron surface, it is possible to carry out the electrochemical grafting of a polyacrylate with a low molar mass the acrylate unit of which contains a chemical function allowing the subsequent polymerization of another monomer. For example, ethyl 2-chloropropionate acrylate allows the initiation of polymerization of the styrene by Atom Transfer Radical Polymerization (ATRP) (Claes et al., 2003), norbornenylmethylene acrylate offers the possibility of polymerizing norbornene by ring opening metathesis polymerization (ROMP) (Detrembleur et al., 2001) and 2-phenyl-2-(2,2,6,6-tetramethyl-piperidin-1-yloxy)-ethylacrylate (PTEA) makes the polymerization of styrene possible, thanks to the presence of alkoxyamine (polymerization initiator) according to the nitroxide mediated process (NMP) (Voccia et al., 2003).